adb: kill adb_thread_{create, join, detach, exit}.

We have std::thread now, so we can delete this cruft.

Test: python test_device.py
Test: adb_test
Test: wine adb_test.exe
Test: /data/nativetest/adbd_test/adbd_test
Change-Id: Ie1c1792547b20dec45e2a62ce6515fcb981c3ef8